Many avionics systems use at least one electronic power supply which is required to operate when energized with an input voltage varying over a very wide input voltage range. In these systems (typically found in an aircraft), the power supplies are energized from a Permanent Magnet Generator (PMG), which is typically mounted via gear box to the (aircraft) engine and outputs a voltage generally proportional to the speed of the engine. It is usually required to have the avionics equipment commence operation while the engine speeds and PMG output/power converter input voltages are very low, and continue to operate as the converter input voltage increases to some maximum, determined by the maximum engine speed. To operate over this large range of input voltage, it has often been necessary to cascaded plural power converter stages, so as to successively reduce the input voltage ranges in stages, down to manageable levels, with the last converter stage then providing the necessary filtering, isolation, scaling and regulation for the avionics system. If active power factor correction is also required, an additional pre-regulator converter is cascaded with the cascade of power conversion stages. As is well known, multiple power conversion stages reduce efficiency, increase cost, and increase size of the power supply system.
It is therefore highly desirable to provide a power supply converter having a single stage, which will achieve a required DC output voltage with some degree of regulation for a very large input voltage range. It is also desirable to provide a single stage power converter which has a good input-to-output isolation, while attaining a high efficiency (typically, greater than 80%). For power factor correction applications, this push-pull converter, by transitioning between the Boost and Buck operating modes, is able to shape the input current.